 Pete LePage [X](https://twitter.com/petele) [GitHub](https://github.com/petele) [Mastodon](https://techhub.social/@petele) [Homepage](https://petelepage.com/)  Thomas Steiner [GitHub](https://github.com/tomayac) [LinkedIn](https://www.linkedin.com/in/thomassteinerlinkedin) [Mastodon](https://toot.cafe/@tomayac) [Bluesky](https://bsky.app/profile/tomayac.com) [Homepage](https://blog.tomayac.com/)
Published: December 18, 2018
Browser Support
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[Source](https://developer.mozilla.org/docs/Web/API/WakeLock)
> [!TIP]
> **Success:** The Screen Wake Lock API, part of Google's [capabilities project](https://developer.chrome.com/blog/capabilities), launched in Chrome 84.
## What is the Screen Wake Lock API?
To avoid draining the battery, most devices quickly go to sleep when left
idle. While this is fine most of the time, some applications need to keep the
screen awake to complete their work. Examples include cooking apps
that show the steps of a recipe or a game
like [Ball Puzzle](https://ball-puzzle.appspot.com/), which uses the device
motion APIs for input.
The [Screen Wake Lock API](https://w3c.github.io/wake-lock/) provides a way to prevent the device from dimming
and locking the screen. This
capability enables new experiences that, until now, required a platform-specific app.
The Screen Wake Lock API reduces the need for hacky and potentially
power-hungry workarounds. It addresses the shortcomings of an older API
that was limited to keeping the screen on and had a number of
security and privacy issues.
## Suggested use cases for the Screen Wake Lock API
[RioRun](https://www.theguardian.com/sport/2016/aug/06/rio-running-app-marathon-course-riorun),
a web app developed by [The Guardian](https://www.theguardian.com/),
was a perfect use case (though it's no longer available).
The app takes you on a virtual audio tour of Rio, following the route of the 2016
Olympic marathon.
Without wake locks, users' screens would turn off frequently while the tour played,
making it hard to use.
Of course, there are plenty of other use cases:
- A recipe app that keeps the screen on while you bake a cake or cook dinner
- A boarding pass or ticket app that keeps the screen on until the barcode has been scanned
- A kiosk-style app that keeps the screen on continuously
- A web-based presentation app that keeps the screen on during a presentation
> [!TIP]
> **Success:** After implementing the Screen Wake Lock API, *Betty Crocker* , a major cooking site in the US, saw a 300% increase in purchase intent indicators for their users. Read more in the 🍰 [Betty Crocker case study](https://web.dev/case-studies/betty-crocker).
## Use the Screen Wake Lock API
The Screen Wake Lock API provides just one type of wake lock: `screen`.
#### `screen` wake lock
A `screen` wake lock prevents the device's screen from turning
off so that the user can see the information that's displayed on screen.
> [!CAUTION]
> **Caution:** An earlier version of the specification allowed an additional `system` wake lock that prevents the device's CPU from entering standby mode, so that your app can continue running. We aren't proceeding with this type.
### Get a screen wake lock
To request a screen wake lock, you need to call the `navigator.wakeLock.request()`
method that returns a `WakeLockSentinel` object. Optionally, you can pass the
type, `screen`, as a parameter. The browser can refuse the request for various
reasons (for example, because the battery charge level is too low),
so it's a good practice to wrap the call in a `try...catch` statement.
The exception's message contains more details in case of failure.
### Release a screen wake lock
You also need a way to release the screen wake lock, which is achieved by calling the
`release()` method of the `WakeLockSentinel` object.
If you don't store a reference to the `WakeLockSentinel`, there's no way
to release the lock manually, but it will be released once the current tab is invisible.
If you want to automatically release the screen wake lock
after a certain period of time has passed,
you can use `window.setTimeout()` to call `release()`, as shown in the example.
// The wake lock sentinel.
let wakeLock = null;
// Function that attempts to request a screen wake lock.
const requestWakeLock = async () => {
try {
wakeLock = await navigator.wakeLock.request();
wakeLock.addEventListener('release', () => {
console.log('Screen Wake Lock released:', wakeLock.released);
});
console.log('Screen Wake Lock released:', wakeLock.released);
} catch (err) {
console.error(`${err.name}, ${err.message}`);
}
};
// Request a screen wake lock...
await requestWakeLock();
// ...and release it again after 5s.
window.setTimeout(() => {
wakeLock.release();
wakeLock = null;
}, 5000);
The `WakeLockSentinel` object has a property called `released` that
indicates whether a sentinel has already been released.
Its value is initially `false`, and changes to `true` once a `"release"`
event is dispatched. This property helps web developers know when a lock
has been released, without manual tracking.
### The screen wake lock lifecycle
When you play with the [screen wake lock demo](https://googlechrome.github.io/samples/wakelock/), you can see that screen
wake locks are sensitive to [page visibility](https://developer.mozilla.org/docs/Web/API/Page_Visibility_API).
This means that the screen wake lock is automatically released when you minimize
a tab or window, or switch away from a tab or window where a screen wake lock is active.
To reacquire the screen wake lock,
listen for the [`visibilitychange`](https://developer.mozilla.org/docs/Web/API/Document/visibilitychange_event) event
and request a new screen wake lock when they occur:
const handleVisibilityChange = async () => {
if (wakeLock !== null && document.visibilityState === 'visible') {
await requestWakeLock();
}
};
document.addEventListener('visibilitychange', handleVisibilityChange);
## Minimize your impact on system resources
Should you use a screen wake lock in your app?
The approach you take depends on the needs of your app. Regardless, you should
use the most lightweight approach possible for your app to minimize its
impact on system resources.
Before adding a screen wake lock to your app, consider whether your use cases could
be solved with one of the following alternative solutions:
- If your app is performing long-running downloads, consider using [background fetch](https://developer.chrome.com/blog/background-fetch).
- If your app is synchronizing data from an external server, consider using [background sync](https://developer.chrome.com/blog/background-sync).
> [!NOTE]
> **Note:** Like most web APIs, the Screen Wake Lock API is only available when served over `HTTPS`.
### Demo
Check out the [Screen Wake Lock demo](https://googlechrome.github.io/samples/wakelock/) and [demo source](https://github.com/GoogleChrome/samples/tree/gh-pages/wakelock).
Notice how the screen wake lock is automatically released when you switch tabs
or apps.
### Screen Wake Locks in the OS task manager
You can use your operating system's task manager to see if an application is preventing
your computer from sleeping. The video shows the macOS
[Activity Monitor](https://support.apple.com/guide/activity-monitor/welcome/mac)
indicating that Chrome has an active screen wake lock that keeps the system awake.
## Feedback
Did you find a bug with Chrome's implementation? Or is the implementation
different from the spec?
- [File a bug](https://issues.chromium.org/issues/new?noWizard=true&template=1942902&component=1456964). Include as much detail as you can. Provide clear instructions for reproducing the bug, and set *Components* to `Blink>WakeLock`.
## Resources
- Specification [Candidate Recommendation](https://www.w3.org/TR/wake-lock/) \| [Editor's Draft](https://w3c.github.io/wake-lock/)
- [Screen Wake Lock Demo](https://googlechrome.github.io/samples/wakelock/) \| [Screen Wake Lock Demo source](https://github.com/GoogleChrome/samples/tree/gh-pages/wakelock)
- [Tracking bug](https://bugs.chromium.org/p/chromium/issues/detail?id=257511)
- [ChromeStatus.com entry](https://www.chromestatus.com/feature/4636879949398016)
- [Experimenting with the Wake Lock API](https://medium.com/dev-channel/experimenting-with-the-wake-lock-api-b6f42e0a089f)
- Blink Component: [`Blink>WakeLock`](https://chromestatus.com/features#component%3ABlink%3EWakeLock)
## Acknowledgements
Task manager video courtesy of
[Henry Lim](https://twitter.com/henrylim96/status/1359914993399959559).